1. Field of the Invention
This invention relates to an impact-resistant resin composition having excellent mechanical strength, and good luster, shapability and weatherability, as well.
More specifically, the present invention relates to an impact-resistant resin composition having excellent mechanical strength, shapability and weatherability which comprises a graft copolymer (A) obtained by the bulk-suspension polymerization of an aromatic monoalkenyl monomer and a vinyl cyan monomer in the presence of a diene type rubber component and having dispersed therein rubbers of a specific particle size, a graft copolymer (B) obtained by the emulsion-polymerization of the above-mentioned monomers and a mixture of said monomers and an alkyl ester monomer of (meth)acrylic acid in the presence of a diene type rubber latex, and a chlorinated polyethylene (C) having a degree of chlorination of from 25 to 45% by weight.
2. Description of Prior Arts
An impact-resistant resin prepared from a butadiene type rubber component, an aromatic monoalkenyl monomer and a vinyl cyan monomer is referred to as an ABS resin and has gained broad applications because of its excellent mechanical properties and moldability.
As typical production methods of this ABS resin, the bulk-suspension polymerization method and the emulsion polymerization method have been well known.
In producing the ABS resin by the emulsion polymerization method, for example, the copolymerization is effected whereby the vinyl monomer is grafted to the rubber latex. Hence, it is possible to optionally vary the rubber content in the resin. Since the particle size of the rubber latex is generally small, however, the resulting resin has a small mechanical strength in comparison with the rubber content in the resin. Moreover, an emulsifier, a coagulating agent and the like used during the production process persistently remain in the resin, and the ABS having a high impact-resistance produced by the emulsion polymerization method is inferior with respect to its weatherability and thermal stability.
Further, the ABS resin prepared by the bulk-suspension polymerization method does not contain impurities such as the abovementioned emulsifier, and has excellent thermal stability. In the bulk-suspension polymerization method, however, the diene type rubber component is dissolved in the vinyl monomer and thus subjected to the polymerization so that it may be not easy to obtain an ABS resin having a high rubber concentration. In addition, the particle size of the rubber in the resulting resin is relatively large. Consequently, though the resulting resin exhibits good mechanical strength in comparison with the rubber concentration, an article molded therefrom has a poor luster. Thus, the commercial use of the resin is deteriorated.
On the other hand, it is well known that when chlorinated polyethylene is compounded with styreneacrylonitrile copolymer and ABS resin, the mechanical strength, especially impact resistance, is improved. However, when the chlorinated polyethylene is compounded with the ABS resin prepared by the emulsion polymerization method, the resulting resin composition has remarkably inferior thermal stability and moldability probably because of the presence of impurities such as the aforementioned emulsifier. In order to improve the impact resistance of the resin composition by compounding the chlorinated polyethylene with the ABS resin prepared by the bulk-suspension polymerization method, it is necessary to blend a considerably large amount of the chlorinated polyethylene. For this reason, characteristic properties of the ABS resin produced by the bulk-suspension polymerization method, such as good thermal stability, are deteriorated and at the same time, its heat resistance as well as rigidity are also lowered. It has been found that a resin composition having a good balance of properties can not be obtained.